如何添加类方法 [英] How to prepend classmethods

问题描述

这个问题直接与这个问题有关.但我试图将其分解为基本问题，我不想在另一个问题框中输入更多文本.所以这里是:

This question directly relates to this one. But I tried to break it down to the base problem and I didn't want to enter even more text into the other question box. So here goes:

我知道我可以通过扩展模块 ClassMethods 并通过 Module#include 钩子包含它来包含类方法.但是我可以用 prepend 做同样的事情吗?这是我的例子:

I know that I can include classmethods by extending the module ClassMethods and including it via the Module#include hook. But can I do the same with prepend? Here is my example:

Foo 类:

class Foo
  def self.bar
    'Base Bar!'
  end
end 

类扩展:

module Extensions
  module ClassMethods
    def bar
      'Extended Bar!'
    end
  end

  def self.prepended(base)
    base.extend(ClassMethods)
  end
end
# prepend the extension 
Foo.send(:prepend, Extensions)

FooE 类:

require './Foo'

class FooE < Foo
end

和一个简单的启动脚本:

and a simple startscript:

require 'pry'
require './FooE'
require './Extensions'

puts FooE.bar

当我启动脚本时，我得到的不是 Extended Bar!，而是 Base Bar!.我需要更改什么才能正常工作?

When I start the script I don't get Extended Bar! like I expect but rather Base Bar!. What do I need to change in order to work properly?

推荐答案

问题是，即使你预先准备了模块，ClassMethods 仍然被 extendedin. 你可以这样做来得到你想要的:

The problem is that even though you're prepending the module, ClassMethods is still getting extended in. You could do this to get what you want:

module Extensions
  module ClassMethods
    def bar
      'Extended Bar!'
    end  
  end  

  def self.prepended(base)
    class << base
      prepend ClassMethods
    end  
  end  
end

请注意，Extensions 本身既可以放在 Foo 中，也可以包含在其中.重要的部分是在 ClassMethods 前面加上.

Note that Extensions itself could be either prepended or included in Foo. The important part is prepending ClassMethods.

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